I'm hoping I didn't do something wrong, and I strongly believe I did not, but Pit is very much like you described.
I didn't train him to be calm all the time, but he turned out that way for some reason. He doesn't get excited when people come over, he prefers not to go meet new dogs (although his breed is aloof, so that's fine) but he also doesn't get excited when I come home from a long day of being away. He doesn't get excited to go for walks, to go for car rides, to see people he hasn't seen in a long time.. he's just very calm.
That being said, he was that way right from the start as an 8 week old puppy. This puppy had NO desire to be a puppy, no matter how much I tried to encourage it.
He has moments of life, like when we play fetch in the river, or the first while of being let off leash with Zero, so he's not a zombie or anything. But I think if I had actually trained him to be calm, he could probably be one of those dogs you described that is always calm.
I don't doubt he's a happy dog. I don't know how happy he'd be if he never got to show excitement.